The present invention relates to a multilayer electronic part, its manufacturing method, a two-dimensionally arrayed element packaging structure and its manufacturing method, or in particular a technique for a probe having a multiplicity of two-dimensionally arrayed piezoelectric ceramic transducer elements (multilayer electronic part) suitably used, for example, to attain a high performance of an ultrasonic probe apparatus.
In recent years, an ultrasonic transceiver using a piezoelectric ceramic transducer element has come to be used for various applications. Especially, the ultrasonic diagnostic system which, unlike the X-ray diagnosis, permits the interior of the human body to be observed without adversely affecting the human body has extended widely as medical equipment. The ultrasonic diagnostic system used for the ultrasonic diagnosis method uses a probe having a multiplicity of piezoelectric ceramic transducer elements as an ultrasonic transceiver. The probe configured with piezoelectric ceramic transducer elements includes a scanning probe having a multiplicity of minuscule piezoelectric ceramic transducer elements arranged for diagnosing the interior of the human body by forming tomographic images.
Among these probe structures, with the probe having one-dimensionally arranged piezoelectric ceramic transducer elements, the focal point can be arbitrarily set at a near or far point from the probe by selecting the number of elements arranged in a given direction, while the focal point is fixed in the direction orthogonal to the particular direction, and therefore a clear image cannot be produced in other than the range corresponding to the depth of focus.
In order to solve the disadvantage described above, a two-dimensionally arrayed probe structure having piezoelectric ceramic transducer elements arranged not only in a single direction but also in the direction orthogonal thereto has been developed. Such a probe structure is described, for example, in xe2x80x9c1996, IEEE Ultrasonics Symposium, pp. 1523-1526xe2x80x9d. With this two-dimensional probe structure, a key to achieving a high performance is how the piezoelectric ceramic transducer elements are reduced in size and how densely they are arranged in a limited space. Along with the high-density arrangement, it is important that each of the two-dimensionally arrayed piezoelectric ceramic transducer elements and the electrical connections thereof are free of a defect, i.e. each piezoelectric ceramic transducer element making up the probe is free of a defect.
From this viewpoint, a method of configuring two-dimensionally arranged probe structure configured of modules each having a plurality of elements is described in xe2x80x9c1996 IEEE Ultrasonics Symposium, pp. 1573-1576xe2x80x9d. This publicly known reference discloses a method of constructing a probe structure having 4096 (64xc3x9764) elements of 0.22 mmxc3x970.22 mm as a combination of a plurality of modules each including two columns of 64 elements.
The conventional modular structure disclosed in the aforementioned reference, however, is so configured that a flexible wiring board and a common electrode are connected to the surface of each piezoelectric ceramic transducer element to drive the particular piezoelectric ceramic transducer element. Thus, the elements are not structured independently of each other but bonded to each other. A defective or ill-connected element, if included in the elements that have built up a module, therefore, cannot be independently replaced or the connection failure thereof cannot be repaired easily, thereby leading to the problem of a low yield for each module.
Also, the conventional modular structure presupposes that each piezoelectric ceramic transducer element is configured of a single board (single layer), and no consideration is given of the application to a multilayer piezoelectric ceramic transducer element required for improving the probe performance.
Further, the conventional multilayer piezoelectric ceramic transducer element configured either in such a manner that as shown in FIG. 15, alternate ones of a surface electrode 12, an internal electrode 13xe2x80x2 in ceramics 11 and a back electrode 15 along the thickness of the multilayer are electrically connected to each other by side electrodes 61 formed on the two opposed side surfaces of the element, or in such a manner that as shown in FIG. 16, alternate ones of the surface electrode 12, the internal electrode 13xe2x80x2 and the back electrode 15 are electrically connected to each other alternately along the thickness of the multilayer by a conductive material 62 filled in a through hole. As a result, the production process is comparatively complicated and the size reduction is limited. Also, for connecting the two electrode groups of the element to an external means, the two surfaces of the element are unavoidably used for external connection. Thus, it is difficult to replace the element or repair the connection, thereby making the application to the probe unsuitable.
The present invention has been developed in view of this point, and the object thereof is to provide a two-dimensionally arrayed probe (element packaging structure) in which a multilayer element can be used as a piezoelectric ceramic transducer element and each defective element, if any, can replaced or any ill connection of each element can be repaired on the one hand, and to provide a piezoelectric ceramic transducer element (multilayer electronic part) suitable for realizing such an element packaging structure on the other hand.
In order to achieve the object described above, according to this invention, a multilayer electronic part is configured with, for example, a multilayer chip-like element having a surface electrode, an internal electrode and a back electrode and a flexible board attached to one side surface of the chip-like element, alternate ones of the electrodes along the thickness of the multilayer of the chip-like element are connected electrically to each other by electrode patterns of the flexible board thereby to form two electrode groups, and the end portions of the electrode patterns of the flexible board, for example, are used as two electrode portions for external connection which are electrically connected with the two electrode groups. A plurality of the aforementioned multilayer electronic parts are arranged in columns and rows and integrated into a two-dimensionally arrayed module. As many modules as required are combined to construct a probe for an ultrasonic probe apparatus.
The use of the multilayer piezoelectric ceramic transducer element (the multilayer electronic part described above) makes it possible to produce a compact, high-performance probe. Also, in view of the configuration in which each multilayer electronic part (piezoelectric ceramic transducer element) is provided with two independent electrode portions for external connection, each multilayer electronic part (piezoelectric ceramic transducer element) can be inspected for a defective chip-like element and a connection failure. Thus a defective multilayer electronic part can be replaced and the ill connection of each multilayer electronic part can be repaired easily for each piezoelectric ceramic transducer element (multilayer electronic part). As a result, the defective module is eliminated and a high-yield module production is made possible. Further, the connection for forming two electrode groups of a chip-like element and the formation of electrode portions for external connection are performed by the electrode patterns of the flexible board on one side surface of the chip-like element. Therefore, the production process is simplified and the multilayer electronic part (piezoelectric ceramic transducer element) can be remarkably reduced in size.